Integrated circuit die are conventionally enclosed in plastic packages that provide protection from hostile environments and enable electrical interconnection between the integrated circuit die and printed circuit boards. The elements of such a package include a metal leadframe, an integrated circuit die, bonding material to attach the integrated circuit die to the leadframe, bond wires which electrically connect pads on the integrated circuit die to individual leads of the leadframe, and a hard plastic encapsulant material which covers the other components and forms the exterior of the package.
The leadframe is the central supporting structure of such a package. A portion of the leadframe is internal to the package, i.e., completely surrounded by the plastic encapsulant. Portions of the leads of the leadframe extend eternally from the package and are used to connect the package externally.
Further background information concerning conventional plastic integrated circuit packages and leadframes is contained in chapter 8 of the book Microelectronics Packaging Handbook (1989), which was edited by R. Tummala and E. Rymaszewski, and is published by Van Nostrand Reinhold, 114 Fifth Avenue, New York, N.Y.
A problem with conventional plastic packages is that their internal leadframes limit reduction of the size of the packages. Practitioners have attempted to reduce the size of packages by eliminating internal leadframes, as is shown in U.S. Pat. No. 4,530,142 to Roche et al and U.S. Pat. No. 5,172,214 to Casto, but these packages have numerous disadvantages. The contacts of the package shown by Roche et al. in the '142 patent have orthogonal side surfaces. Accordingly, the packages are believed to be unreliable because the contacts could easily be pulled from the encapsulant material. The package shown by Casto in the '214 patent has bent leads which extend vertically above the die pad to the top of the die. Including such leads in a package would increase manufacturing costs and limit reductions in the lateral size of the package. Accordingly, there is a need for a smaller and more reliable plastic package.